Below are definitions of terms in their most accepted usage. If even thinking about the evolution of humans bothers you, simply apply these terms to animals and plants, and exclude humans from your definition for the time being.

Evolution: Taken in its most basic form, evolution simply means change. The biology textbook1 I teach from defines evolution as "the cumulative genetic changes in a population from generation to generation."

Unfortunately, "evolution" is used at various times to mean microevolution, macroevolution, evolutionary theory, neo-Darwinism and evolutionism, all of which I define below.

Microevolution:
Small changes in the genetics of a population of organisms occurring over successive generations. Many of these genetic changes are reflected in an organism's appearance or internal physiology.

An example of microevolution is seen clearly in the breeding of dogs from a wolf-like ancestor into so many different-looking creatures, as varied as poodles and Great Danes. In the natural world, we see many examples of organisms changing over time through the fossil record, and even within human history. This fact is not contested by anyone.

In a given generation, species produce -- or have the potential to produce -- more offspring than survive.

Individuals differ from one another -- whether in their appearance or their behavior or their internal physiology. Since Darwin's time, scientists have discovered that genes are the inherited factor that makes individuals different from one another. (The environment also causes variation, but natural selection only acts on what is inherited between generations)

Resources in any environment are not infinite, but limited -- whether space, food, light, water, or potential mates. As a result, individuals compete for these limited resources.

Individuals with characteristics that allow them to secure more food, more growing space, or more mates leave disproportionately more offspring in successive generations. Therefore, the "more fit" individuals tend to pass their particular characteristics on because they are most suited to the current environmental conditions.

Macroevolution: Large-scale changes in organisms occurring over long time spans (thousands or millions of years). These changes are thought to have occurred via natural selection, or sometimes through chance genetic mutations. An example of large-scale or macroevolutionary change would be the development of wings with feathers.

Evolutionary biology: The entire body of evolutionary research. Evolutionary biology is an extensive discipline, and there are numerous college departments devoted to its study, such as Rice University's "Department of Ecology and Evolutionary Biology."

Neo-Darwinism: The synthesis of previous theories, especially of Mendelian genetics, with Darwin's theory of evolution by natural selection to formulate a comprehensive explanation of evolution; also called the synthetic theory of evolution. I avoid using this term when teaching because it ends in "ism" which typically means a belief system. "Neo-Darwinism" means something quite different from "Darwinism."

Evolutionism (or Darwinism): The philosophical position that states evolutionary theory is incompatible with belief in God. Evolutionism is often what Christians mean when saying they oppose evolution, although it is often confused with the science of evolution. Evolutionism is an invalid extension of evolutionary biology out of science and into the realm of philosophy.